1. Field of the Invention
The present invention relates generally to control systems for vehicle engines, and more particularly, a system for controlling an engine output adjusting device provided in a vehicle engine, such as a throttle valve, to cause the vehicle engine to have fundamentally a predetermined normal output in accordance with a controlled variable on an accelerator accompanying with the vehicle engine and exceptionally an augmented output on the occasion of an accelerating condition thereof, and then to be restored to have the predetermined normal output after the accelerating operation.
2. Description of the Prior Art
There has been proposed a throttle valve control system which comprises a driving device for actuating a throttle valve provided in a vehicle engine to have a predetermined normal opening degree in accordance with a controlled variable on an accelerator acompanying with the vehicle engine so that intake air mass flow determined by the throttle valve in a predetermined manner is supplied to the vehicle engine and a compensating device for revising the predetermined normal opening degree of the throttle valve to be augmented when an increasing speed of the controlled variable on the accelerator exceeds a predetermined value so as to cause the vehicle engine to work in an accelerating condition thereof, as disclosed in, for example, the Japanese patent application published before examination under publication No. 57-116140. Such a system includes further a restoring device for restoring the throttle valve to have the predetermined normal opening degree corresponding to the controlled variable on the accelerator after the accelerating condition of the vehicle engine is terminated so that the vehicle engine is put back into a normally operating condition.
With the throttle valve control system thus proposed previously, on the occasion of the accelerating operation of the vehicle engine, the throttle valve is actuated to have the augmented opening degree which is set by the compensating device in response to increase in controlled variable on the accelerator so that increased intake air mass flow is supplied to the vehicle engine and therefore an engine output is increased, and then the throttle valve is restored to have the predetermined normal opening degree corresponding to the controlled variable on the accelerator by the restoring device after the accelerating condition of the vehicle engine is terminated. In the event of the restoration of the throttle valve arising after the acceleration of the engine, the throttle valve is shifted from a position corresponding to the augmented opening degree to a position corresponding to the predetermined normal opening degree at a predetermined constant changing speed, and therefore the vehicle engine is changed gradually from the accelerating condition into the normal operating condition.
Accordingly, in the case of a vehicle engine which is equipped with such a previously proposed throttle valve control system as described above, even though an accelerator accompanying with the vehicle engine is released from a control input imposed thereon after a throttle valve is once actuated to have the augmented opening degree in response to increase in controlled variable on the accelerator in an accelerating condition of the vehicle engine occuring, for example, immediately after the starting of a vehicle in which the vehicle engine is employed, the opening degree of the throttle valve is not reduced rapidly and therefore the travelling speed of the vehicle is not reduced for a while. This results in a disadvantage that the responsibility in a travelling speed control of the vehicle is deteriorated.
For the purpose of avoiding such a problem, it is considered to arrange the restoration of the throttle valve arising after the accelerating operation of the vehicle engine to be completed in a short time. However, in such a case, when the control input on the accelerator is ceased from increasing after the throttle valve is actuated to have the augmented opening degree for causing the vehicle engine to be accelerated under a condition wherein the vehicle is travelling at high speed, the vehicle is undesirably prevented from being accelerated immediately in response to the stopping of the accelerator, so that a shock resulting from rapid reduction of the travelling speed is given to the vehicle and the travelling of the vehicle at high speed is made to be lacking in smoothness though the responsibility in the travelling speed control of the vehicle immediately after the starting of the vehicle is improved.